CN111650680A - Preparation method of self-tracing grating standard substance capable of accurately shortening pitch value - Google Patents
Preparation method of self-tracing grating standard substance capable of accurately shortening pitch value Download PDFInfo
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Abstract
The invention relates to a method for preparing a self-tracing grating standard substance capable of accurately shortening a pitch value, which is used for preparing a small-pitch tracing standard substance with the size of hundreds of nanometers and below based on a laser convergence atomic deposition technology and a soft X-ray interference lithography technology and comprises the following steps: 1) obtaining a mask substrate; 2) depositing and preparing a mask on a mask substrate by adopting a laser convergence atomic deposition technology; 3) obtaining a photoresist sample, wherein the photoresist sample comprises a photoresist and a second substrate; exposing and developing the photoresist by adopting a mask plate through a soft X-ray interference photoetching technology to obtain a photoresist grating structure; 4) and transferring the photoresist grating structure to a second substrate to obtain the self-tracing grating standard substance. Compared with the prior art, the self-tracing grating standard substance prepared by the invention has the advantages of high precision, tracing property, precision pitch value shortening and the like.
Description
Technical Field
The invention relates to the field of nano-grating standard substances, in particular to a preparation method of a self-tracing grating standard substance capable of accurately shortening a pitch value.
Background
With the continuous progress of nanotechnology, the characteristic size of the device enters the nanometer level, the uncertainty in the processing and manufacturing process is obviously increased, and the influence of the processing error on the performance of the device is larger and larger. Nano-metering is the basis for measuring and characterizing nano-scale devices, plays an important role in the fields of process control and quality management in the nano-manufacturing process, and is an irretrievable key scientific and technical problem in the fields of MEMS, ultra-precision machining, nano-medicine, nano-biology and the like. The nano-metering is the primary premise of realizing accurate and reliable measurement values of nano-scale, and the difficulty lies in nano-precision and traceability. The traditional commercial test instruments such as SEM, AFM and the like are limited by the working principle and some inherent properties, and the measurement results have measurement errors in a nanometer scale. Different instruments measure the same sample and the results may be quite different. A practical approach to this problem is to use nano-meter delivery criteria. Nano-metering transfer standards are standards of defined geometric dimensions fabricated using specific nano-fabrication techniques. After the measuring instruments such as SEM and AFM are calibrated by the nanometer measurement transfer standard, the measuring result can be traced to the national standard or the SI meter definition, and the accuracy and the reliability of the measurement are greatly improved.
The nano-grating standard substance is a commonly used nano-metering transmission standard, and the preparation process is mainly divided into two types according to traceability: the first kind can not directly trace the basic constant or SI meter definition in nature, such as the traditional photoetching technology, electron beam etching, multilayer film technology and the like, the prepared standard substance has no tracing property, the characteristic value of the standard substance is traced to the measuring instrument of the national measuring mechanism by measuring the value by the national measuring mechanism, and then the commercial instrument can be calibrated by the standard substance; the second type can directly trace to the basic constant or SI meter unit definition in nature, such as the NIST development of the standard substance of the line width based on the silicon lattice and the adoption of the laser convergence atomic deposition technology to prepare the standard substance of the grating with the self-tracing characteristic in the university of Tongji and China metrological science research institute. The self-tracing grating standard substance prepared by the laser convergence atomic deposition (also called atomic photoetching) technology has the advantages that the atomic deposition position and the node (antinode) position of a laser standing wave field are strictly corresponding in the preparation process, the laser wavelength is locked on the known atomic transition energy level by the laser-induced fluorescence frequency stabilization technology, and the pitch of the grating standard substance can be strictly traced to the natural transition frequency between the atomic transition energy levels. The area of the grating area can reach millimeter level, and the method has good consistency in samples and consistency among samples, and is an optimal technical scheme for preparing standard substances with high accuracy and high precision.
In the preparation method of the standard substance, the traditional photoetching technology can prepare a large-area grating standard substance, but the grating pitch is limited by the visible light wavelength used by photoetching, and the minimum pitch value is 200 nm; the pitch of the grating standard substance prepared by the electron beam etching technology can be in the range of hundreds of nanometers to tens of nanometers, but is limited by the limit of etching equipment on the single-field exposure area, and a multi-field splicing mode is usually used for the small-pitch and large-area grating standard substance, so that the requirements on uniformity and traceability are difficult to meet; the multilayer film grating technology can also prepare tens of nanometer standard substances, but the thickness of the film layer can drift along with the increase of the number of the film coating layers under the constraint of the film coating conditions in the preparation technology, and the area of the obtained grating structure area is smaller. More importantly, although the pitch value of the standard substance prepared by the preparation method in the first category can be hundreds of nanometers and tens of nanometers, the preparation process has no traceability, and the calibration needs to be carried out by a measuring instrument of a national measuring institution to ensure that the value is traced to a meter unit definition, so that the traceability chain is long and the uncertainty is large, for example, the pitch value of 100nm standard substance (nominal pitch value of 100nm +/-2 nm) of VLSI Standards is 1 nm. At present, research on nano technology in dimensionality enters ten-nanometer nodes, and a series of high-precision standard substances with magnitude tracing are urgently needed to calibrate measurement in the scales of hundreds of nanometers and tens of nanometers, so that new requirements are provided for a preparation method of the standard substances.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a high-precision and self-tracing preparation method of a self-tracing grating standard substance with a self-tracing property and an accurate shortened pitch value.
The purpose of the invention can be realized by the following technical scheme:
a method for preparing a self-tracing grating standard substance capable of accurately shortening a pitch value is used for preparing a small-pitch tracing standard substance with a hundred-nanometer scale or below based on a laser convergence atomic deposition technology and a soft X-ray interference lithography technology, and comprises the following steps:
a mask substrate obtaining step: the method comprises the steps of obtaining a mask substrate, wherein the mask substrate is divided into a window area and a non-window area, the window area comprises a first substrate, and the non-window area comprises a film layer and a first substrate;
a mask plate preparation step: depositing and preparing a self-tracing mask on the mask substrate by adopting a laser convergence atomic deposition technology;
the preparation method of the photoresist grating structure comprises the following steps: obtaining a photoresist sample, wherein the photoresist sample comprises a photoresist and a second substrate; exposing the photoresist by adopting the self-tracing mask plate through a soft X-ray interference photoetching technology, and then obtaining a photoresist grating structure through a developing process;
acquiring a grating standard substance: and transferring the photoresist grating structure to the second substrate to obtain the grating standard substance.
Furthermore, in the step of preparing the photoresist grating structure, the grating diffraction light level of the soft X-ray interference photoetching technology is first level or second level.
Furthermore, in the step of obtaining the mask substrate, the window regions are transparent to X-rays, the non-window regions are opaque to X-rays, the number of the window regions is two, and the two window regions are the same in size and are symmetrically distributed.
Further, the soft X-ray adopted by the soft X-ray interference lithography technology has coherence, and when the grating diffraction light order is one order, two window regions satisfy:
d is more than or equal to 0.2L, and D +2L is less than or equal to LC
Wherein D is the width of the middle region of the two window regions, L is the width of the window region, LCIs the coherence length of the soft X-ray passing through the mask;
when the grating diffraction light order is two-order, two window areas satisfy:
d is not less than 3L, and D +2L is not more than LC，L≤300μm。
Further, in the step of preparing the photoresist grating structure, when the grating diffraction light order is first order, the peak-to-valley height value H of the photoresist grating structure satisfies:
the full width at half maximum FWHM of the photoresist grating structure satisfies:
when the grating diffraction light order is two-level, the peak-to-valley height value H of the photoresist grating structure satisfies the following condition:
the full width at half maximum FWHM of the photoresist grating structure satisfies:
in the formula, P0Is the pitch value of the grating structure in the mask.
Further, in the step of obtaining the mask substrate, the film thickness h of the mask substrate satisfies the following condition: h is more than or equal to 50nm and less than or equal to 300nm, the surface roughness of the film layer is better than 0.3nm, and the maximum height value of the surface profile of the film layer is lower than 2 nm.
Furthermore, in the step of preparing the mask, the atomic species adopted by the laser convergence atomic deposition technology are chromium atoms, aluminum atoms or iron atoms.
Further, in the step of preparing the photoresist grating structure, the divergence angle of a light source adopted by the soft X-ray interference lithography technology is less than 1mrad, the grating structure is formed in the mask, and the pitch value of the grating structure is more than three times of the wavelength of the light source.
Further, in the step of obtaining the grating standard substance, a reactive ion beam etching process is adopted to transfer the photoresist grating structure to the second substrate.
Further, in the grating standard substance obtaining step, the photoresist is made of PMMA, HSQ or ZEP, and the second substrate is made of silicon, silicon nitride, aluminum or chromium.
Compared with the prior art, the invention has the following advantages:
(1) according to the invention, a self-tracing grating prepared by laser convergence atomic deposition is used as a mask, after interference exposure and subsequent development are carried out on photoresist by using soft X-rays, a photoresist grating structure is transferred onto a substrate through reactive ion beam etching, and a grating standard substance which has tracing property, small pitch and large-area uniformity and can be stably stored for long time is obtained; the self-tracing grating standard substance prepared by the laser convergence atomic deposition technology has tracing performance because the grating pitch value traces the atomic transition energy level in the preparation process, and meanwhile, the grating pitch precision is high, the uncertainty is better than 0.1nm, but the grating pitch value is limited by the used laser wavelength and the atomic species, and the grating pitch value is larger;
the invention further adopts the soft X-ray interference photoetching technology, solves the problem of larger grating pitch value, and can accurately shorten the pitch value;
the method provided by the invention overcomes the problem of single pitch value of the self-tracing grating, inherits the advantages of high precision, tracing property, accurate shortening of the pitch value and the like, and provides a preparation scheme of a small-pitch standard substance with tracing property of hundreds of nanometers and below and high precision;
specifically, in the aspect of pitch value of the standard substance, on the basis of the laser convergence atomic deposition technology, the preparation method can provide the standard substance with the pitch of hundreds of nanometers and below, and the prepared pitch value of the standard substance is exactly equal to the pitch value of the self-tracing grating standard substance prepared by the laser convergence atomic deposition technology
The application of the standard substance of the self-tracing grating is expanded;
in the aspect of standard substance traceability, compared with the traditional photoetching technology, electron beam etching and multilayer film technology, the standard substance has traceability, the value of the standard substance is traced from a self-tracing grating standard substance, and the traceability of the grating value is ensured;
in the aspect of standard substance precision, compared with the traditional photoetching technology, electron beam etching and multilayer film technology, the standard substance has high pitch value precision, the uncertainty is superior to 0.5nm, and the requirement on high-precision standard substances is met;
in the aspect of structural uniformity of a standard substance, compared with electron beam etching and multilayer film technology, the grating region of the standard substance has excellent uniformity, and the area size can reach hundreds of microns;
(2) in the processing step of the mask substrate, the mask substrate is divided into a window area and a non-window area, the window area only comprises a first substrate, the first substrate usually selects a silicon substrate with the thickness of 290 mu m, and when the mask substrate is adopted for interference, the background light of an interference photoetching area in the window area is extremely weak, so that the contrast of interference fringes is improved, and the development of an interference photoetching experiment is facilitated;
(3) the mask prepared by the invention needs to meet the optical characteristics of X-rays, wherein the most important thing is that the X-ray diffraction efficiency and the grating diffraction efficiency are closely related to the grating material and the grating structure characteristics (height, width and bottom layer), and meanwhile, the bottom layer of the metal grating has strong absorption to the X-rays and needs to reduce the influence thereof; the selection conditions of the peak-valley height value and the full width at half maximum of the photoresist grating structure provided by the invention can effectively weaken the influence of the bottom layer of the metal grating on the X-ray absorption;
(4) the invention provides the selection condition of the geometric dimension of the mask substrate for the soft X-ray interference lithography technology, thereby ensuring the structural quality of the exposure grating and balancing the interference of the high-order diffracted light on the exposure area; while soft X-ray light coherence is taken into account.
Drawings
FIG. 1 is a cross-sectional view of a side of a reticle substrate of the present invention;
FIG. 2 is a cross-sectional view of the front side of a reticle substrate of the present invention;
FIG. 3 is a schematic illustration of a laser focused atomic deposition technique of the present invention;
FIG. 4 is a schematic diagram of soft X-ray interference lithography according to the present invention, with cross-sections in phantom;
FIG. 5 is a schematic diagram of the graph transfer of the grating structure by reactive ion beam etching according to the present invention, wherein the hatched portion is a cross-section;
FIG. 6 is a schematic flow chart of a method for manufacturing a nano-grating standard substance with a reduced grating pitch value according to the present invention;
in the figure, 1, a film layer, 2, a first substrate, 3, a non-window area, 4, a window area, 5, an atomic beam, 6, laser, 7, a laser standing wave field, 8, a grating structure, 9, X-ray light, 10, diffracted light, 11, photoresist, 12, a second substrate, 13, a photoresist grating structure, 14, a reactive ion beam etching process, 15 and a grating standard substance.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
Example 1
As shown in fig. 6, the present embodiment provides a method for preparing a self-tracing grating standard substance with an accurately shortened pitch value, which includes the following steps:
reticle substrate acquisition step S1: the method comprises the steps of obtaining a mask substrate, wherein the mask substrate is divided into a window area and a non-window area, the window area comprises a first substrate, and the non-window area comprises a film layer and a first substrate;
the window area is transparent to X-rays, the non-window area is not transparent to X-rays, the number of the window areas is two, the two window areas are the same in size and are symmetrically distributed, and the two window areas are located in the center area of the mask substrate.
The film thickness h of the mask substrate meets the following requirements: h is more than or equal to 50nm and less than or equal to 300nm, the surface roughness of the film layer is better than 0.3nm, and the maximum height value of the surface profile of the film layer is lower than 2 nm.
Mask preparation step S2: depositing and preparing a mask on a mask substrate based on a laser convergence atomic deposition technology;
the atomic species adopted by the laser convergence atomic deposition technology are chromium atoms, aluminum atoms or iron atoms;
photoresist grating structure preparation step S3: obtaining a photoresist sample, wherein the photoresist sample comprises a photoresist and a second substrate; exposing the photoresist by using a mask through a soft X-ray interference lithography technology, and then obtaining a photoresist grating structure through a developing process;
the diffraction light order of the grating of the adopted soft X-ray interference photoetching technology is first order or second order.
Grating standard substance obtaining step S4: and transferring the photoresist grating structure to a second substrate by adopting a reactive ion beam etching process to obtain a grating standard substance.
The expression of the pitch value of the grating standard substance is as follows:
in the formulaP is the pitch value of the grating standard substance, P0The pitch value of the grating structure in the mask is shown, and N is the diffraction light order of the grating.
Some limitations of the preparation method of this example are described in detail below:
the soft X-ray adopted by the soft X-ray interference lithography technology has coherence, and when the grating diffraction light level is one level, the two window areas meet the following conditions:
d is more than or equal to 0.2L, and D +2L is less than or equal to LC
Wherein D is the width of the middle region of the two window regions, L is the width of the window region, LCIs the coherence length of the soft X-ray passing through the mask;
when the grating diffraction light order is two-order, the two window areas satisfy:
d is not less than 3L, and D +2L is not more than Lc，L≤300μm。
When the diffraction light order of the grating is the first order, the peak-valley height value H of the photoresist grating structure satisfies the following condition:
the full width at half maximum FWHM of the photoresist grating structure satisfies:
when the diffraction light order of the grating is two-level, the peak-valley height value H of the photoresist grating structure satisfies the following condition:
the full width at half maximum FWHM of the photoresist grating structure satisfies:
in the formula, P0Is the pitch value of the grating structure in the mask.
The divergence angle of a light source adopted by the soft X-ray interference photoetching technology is less than 1mrad, a grating structure is formed in a mask plate, and the pitch value of the grating structure is more than three times of the wavelength of the light source.
The photoresist comprises PMMA, HSQ or ZEP, and the mask substrate comprises silicon, silicon nitride, aluminum or chromium.
The method comprises the following specific implementation steps:
after the method for preparing the self-tracing grating standard substance capable of accurately shortening the pitch value is implemented, the tracing standard substance with the size of hundreds of nanometers and below can be prepared, and the pitch value of the standard substance is accurately equal to that of the self-tracing grating standard substance
N is diffraction order, and has the characteristics of high precision and small uncertainty, and the method realizes the preparation of the standard substance and adopts the following implementation steps:
firstly, designing and processing a proper mask substrate.
As shown in fig. 1, the whole mask substrate is composed of a film layer 1 and a substrate 2, the substrate is located below the film layer, the substrate plays a role of supporting the film layer, the film layer is not easy to break, and the size in fig. 1 does not represent the real size.
The film layer is made of materials such as silicon nitride, silicon and the like, the thickness is within the range of 50 nm-300 nm, the silicon nitride film layer with the thickness of 100nm is usually selected, and the silicon nitride film layer can be in an amorphous state. The film should be chosen to have low stress and not too thin a thickness, which is likely to crack due to local temperature imbalance caused by long exposure to high flux synchrotron radiation light sources.
The substrate is made of materials such as silicon nitride, silicon and the like, the material selection is to select the etching rate ratio with the film layer material, the thickness of the substrate is in the range of 100-500 mu m, generally, the silicon substrate with the thickness of 290 mu m is selected, and the substrate can be amorphous silicon or monocrystalline silicon. The parameters of the silicon substrate are selected according to the convenience of windowing treatment, the windowing treatment is to use a chemical etching means on the side of the silicon substrate to completely etch partial regions of the silicon substrate material to the silicon nitride film layer, only the silicon nitride film layer is left, and the region only the silicon nitride film layer is left is called a window region 4. Light of X-rays can pass through the window portion, the non-window region 3 (light blocking region) cannot pass at all due to the shielding of the silicon substrate,
as shown in fig. 2. According to the design scheme of the mask substrate, the background light of the interference photoetching area is extremely weak, the contrast of interference fringes is improved, and the development of interference photoetching experiments is facilitated.
In the windowing process, the chemical etching scheme used is not unique, and the critical is the geometrical size of the two window structures after etching. Specifically, the geometric dimensions refer to the width L of each window, and the width D of the opaque portion in the middle of the two windows, as shown in fig. 2. The widths L and D determine the exposure field size and the exposure quality, on the other hand, how to choose a scheme depending on the interference lithography. The surface topography of the silicon nitride film layer is another important parameter in the step, and comprises surface roughness and maximum height value of the contour, wherein the surface roughness is better than 0.3nm, and the maximum height of the contour is not more than 2 nm. Since the silicon nitride surface topography affects the quality of the native grating standard in the second step below, the large surface roughness and profile maximum height can lead to a deterioration of the quality of the mask grating and its optical properties for X-rays.
And secondly, preparing the self-tracing grating standard substance into a mask. And depositing and preparing a self-tracing grating structure on the mask substrate which is processed and designed based on a laser convergence atomic deposition technology to serve as a mask for subsequent interference lithography. The principle of the laser convergent atomic deposition technology is shown in fig. 3, a near-resonance laser standing wave field 7 formed by two lasers 6 with the same parameters and opposite directions interacts with an atomic beam 5 with high collimation degree, so that the spatial distribution of the atomic beam presents periodic distribution, the periodicity of the energy distribution of the period and the laser standing wave field is equal, and then the atomic beam is deposited on a mask substrate to form a grating structure 8, namely a mask plate for interference lithography. The period of the prepared grating structure is equal to half of the wavelength value of laser, and meanwhile, in an experiment, the laser frequency is locked on the transition energy level of atoms by a laser-induced fluorescence frequency stabilization technology, and the transition energy level of the atoms depends on the species and the structure of the atoms and is independent of external environmental conditions and is an accurately known natural constant. Therefore, the grating structure period is traced to the known natural constant of the atomic transition frequency, and the grating is further called as a self-tracing standard substance.
The pitch value of the standard substance is traceable and high in precision, and simultaneously, the standard substance serving as a mask must meet the optical characteristics of X-rays, wherein the most important is the X-ray diffraction efficiency. The diffraction efficiency of the grating is closely related to the grating material and the structural features (height, width and background layer) of the grating, and the background layer of the metal grating has strong absorption to the X-ray, so that the influence of the X-ray is required to be reduced.
For convenience, the metal Cr self-tracing grating (pitch 212.8nm) is used as a mask and the 13.4nm soft X-ray is used as an exposure light source for illustration, but the scope of the invention is not limited thereto.
In order to weaken the influence of the bottom layer on X-ray absorption, the experimental conditions for preparing the mask plate grating are as follows: the transverse size of the pre-collimation slit is 0.5mm multiplied by 2mm, the power of the laser standing wave field is 50mW, and the beam waist diameter of the light spot is 200 mu m; the laser cooling power is 25mw, and the spot size is 2mm × 24 mm. At this time, the ratio of the thickness B of the background layer to the height H of the grating peak valley reaches an optimized value, which is about 1.
Selection of grating peak-to-valley height H and grating full Width half maximum fwhm (full Width at halfmax) with B/H ═ 1: the grating peak-valley height value is within the range of 10-150 nm, the optimal height value is 30nm and 65nm, the maximum diffraction efficiency is realized on X-ray with the wavelength of 13.4nm, and the grating peak-valley height value and the optimal height value respectively correspond to a first-order interference photoetching scheme and a second-order interference photoetching scheme in the third step; the full width at half maximum FWHM of the grating is within 30-180 nm, the optimal width values are 106nm and 140nm, the maximum diffraction efficiency is realized on X-ray with the wavelength of 13.4nm, and the maximum diffraction efficiency respectively corresponds to the first-order and second-order same-interference photoetching schemes in the third step.
And thirdly, carrying out soft X-ray interference lithography exposure, taking the self-tracing grating standard substance as a mask, carrying out soft X-ray exposure and subsequent development on photoresist to obtain a photoresist grating structure, and further etching the obtained photoresist structure pattern on a substrate below the photoresist by using reactive ion beam etching to obtain the small-pitch grating standard substance. Soft X-ray interference lithographyAs shown in fig. 4, coherent X-ray light 9 from top to bottom is diffracted by a self-tracing grating standard substance to form diffracted light 10 which respectively passes through a left window and a right window, and is interfered at a certain space position behind a mask plate to form interference fringes, and the interference fringes expose a photoresist 11 and a photoresist grating structure 13 is obtained after a developing process. The incident light of the coherent X-ray light source is near-parallel light, the divergence angle is less than 1mrad, the wavelength range is 1-20 nm, and the pitch value of the mask is 3 times greater than the wavelength of the light source; the photoresist used is PMMA, HSQ, ZEP or other relatively sensitive photoresist, PMMA being generally selected, and may be spin coated onto substrate 12, which may be Si3N4Si, Cr, Mo, etc., and the Si material is usually selected. And (3) a developing process: after developing for 45s with developer MIBK IPA 1:3, the sample surface was rinsed with 95% absolute ethanol for 30s and then slowly blown dry with nitrogen.
Before reactive ion beam etching, the sample needs to be baked for 30s at 70 ℃ so as to remove water vapor on the surface of the sample and ensure the etching quality. As shown in fig. 5, a reactive ion beam etching process 14 is used to transfer the photoresist structure 13 onto the substrate 12, resulting in a fine pitch grating standard 15. The gas for etching the silicon substrate is SF6And C4H8The RF power is 13W, the ICP power is 400W, the etching time is 25-40 s, and then O is used2And removing the photoresist on the surface of the silicon substrate, and etching for 120 s.
In this step of interference lithography, the diffraction equation P is calculated according to0sin theta is equal to N lambda, and the fringe period formed by the interference of the two diffracted lights (10)
Derived to obtain
Wherein P is0Is the pitch value, P, of the mask grating1Is the pitch value of the photoresist grating after exposure, N is the grating diffraction light order, and theta is the grating diffraction angle; due to the limitation of diffraction efficiency of the grating, N is 1 or 2. Interference photoetching to prepare target according to diffraction orderThe quasi-substance scheme is classified into a first-order interference lithography scheme (N ═ 1) and a second-order interference lithography scheme (N ═ 2).
For the first-order interference photoetching scheme, the selection of the geometric dimension of the mask plate substrate needs to meet the condition that D is more than or equal to 0.2L, so that the structural quality of an exposure grating is ensured, and the interference of high-order diffracted light on an exposure area is balanced; meanwhile, considering the coherence of the soft X-ray light, D +2L is not more than LC，LCIs the coherence length of the soft X-ray (at the mask grating position). The mask grating structure is selected, the peak-valley height value H of the grating is optimally 30nm, and the full width at half maximum FWHM of the grating is optimally 106 nm. The thickness of the PMMA photoresist is 60-80 nm, and the height-width ratio of the photoresist structure is not more than 2.
For the second-order interference photoetching scheme, the selection of the geometric dimension of the mask plate substrate needs to meet the condition that D is more than or equal to 3L, and the exposure area is ensured not to be interfered by first-order and high-order diffracted light; considering the coherence of X-ray, D +2L is not more than LC，LCIs the coherence length of the soft X-ray (at the mask grating location); in addition, in order to ensure the consistency of the grating height, the window width L is less than or equal to 300 mu m. The mask grating structure is selected, the peak-to-valley height H of the grating is optimally 65nm, the full width at half maximum FWHM of the grating is optimally 140nm, and the FWHM needs to have good consistency. The thickness of the PMMA photoresist is 30-50 nm, and the height-width ratio of the photoresist structure is not more than 2.
According to the above two schemes, grating standard substance (15) with pitch value of 106.4nm (first order interference) or 53.2nm (second order interference) can be obtained respectively.
The embodiment can prepare the standard substance with the scale of hundreds of nanometers and below, the pitch value of the standard substance is exactly equal to 1/2N of the pitch value of the self-tracing standard substance, N is diffraction order (N is 1,2), and the standard substance grating structure prepared by the method has the advantages of uniformity in a large area range, pitch value from hundreds of nanometers to tens of nanometers, high precision, tracing property and the like.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (10)
1. A method for preparing a self-tracing grating standard substance capable of accurately shortening a pitch value is characterized in that the method is used for preparing a small-pitch tracing standard substance with the scale of hundreds of nanometers and below based on a laser convergence atomic deposition technology and a soft X-ray interference lithography technology, and the method comprises the following steps:
a mask substrate obtaining step: the method comprises the steps of obtaining a mask substrate, wherein the mask substrate is divided into a window area and a non-window area, the window area comprises a first substrate, and the non-window area comprises a film layer and a first substrate;
a mask plate preparation step: depositing and preparing a self-tracing mask on the mask substrate by adopting a laser convergence atomic deposition technology;
the preparation method of the photoresist grating structure comprises the following steps: obtaining a photoresist sample, wherein the photoresist sample comprises a photoresist and a second substrate; exposing the photoresist by adopting the self-tracing mask plate through a soft X-ray interference photoetching technology, and then obtaining a photoresist grating structure through a developing process;
acquiring a grating standard substance: and transferring the photoresist grating structure to the second substrate to obtain the grating standard substance.
2. The method for preparing a self-tracing grating standard substance capable of accurately shortening the pitch value according to claim 1, wherein in the step of preparing the photoresist grating structure, the grating diffraction light order of the soft X-ray interference lithography technology is first order or second order.
3. The method for preparing a self-tracing grating standard substance capable of accurately shortening the pitch value according to claim 2, wherein in the step of obtaining the mask substrate, the window regions are transparent to X-rays, the non-window regions are opaque to X-rays, the number of the window regions is two, and the two window regions have the same size and are symmetrically distributed.
4. The method for preparing self-tracing grating standard substance for accurately shortening the pitch value according to claim 3, wherein the soft X-ray interference lithography adopts soft X-ray with coherence, and when the diffraction order of the grating is one order, two window regions satisfy:
d is more than or equal to 0.2L, and D +2L is less than or equal to LC
Wherein D is the width of the middle region of the two window regions, L is the width of the window region, LCIs the coherence length of the soft X-ray passing through the mask;
when the grating diffraction light order is two-order, two window areas satisfy:
d is not less than 3L, and D +2L is not more than LC，L≤300μm。
5. The method for preparing a self-tracing grating standard substance capable of accurately shortening the pitch value according to claim 2, wherein in the step of preparing the photoresist grating structure, when the grating diffraction light order is one order, the peak-to-valley height value H of the photoresist grating structure satisfies:
the full width at half maximum FWHM of the photoresist grating structure satisfies:
when the grating diffraction light order is two-level, the peak-to-valley height value H of the photoresist grating structure satisfies the following condition:
the full width at half maximum FWHM of the photoresist grating structure satisfies:
in the formula, P0Is the pitch value of the grating structure in the mask.
6. The method for preparing the self-tracing grating standard substance capable of accurately shortening the pitch value according to claim 1, wherein in the step of obtaining the mask substrate, the film thickness h of the mask substrate satisfies the following condition: h is more than or equal to 50nm and less than or equal to 300nm, the surface roughness of the film layer is better than 0.3nm, and the maximum height value of the surface profile of the film layer is lower than 2 nm.
7. The method for preparing a self-tracing grating standard substance capable of accurately shortening the pitch value according to claim 1, wherein in the step of preparing the mask, the atomic species adopted by the laser convergence atomic deposition technology is chromium atoms, aluminum atoms or iron atoms.
8. The method for preparing a self-tracing grating standard substance capable of accurately shortening the pitch value according to claim 1, wherein in the step of preparing the photoresist grating structure, the divergence angle of a light source adopted by the soft X-ray interference lithography technology is less than 1mrad, the grating structure is formed in the mask, and the pitch value of the grating structure is more than three times of the wavelength of the light source.
9. The method for preparing a self-tracing grating standard substance capable of accurately shortening the pitch value according to claim 1, wherein in the step of obtaining the grating standard substance, a reactive ion beam etching process is adopted to transfer the photoresist grating structure to the second substrate.
10. The method for preparing self-tracing grating standard substance capable of accurately shortening pitch value according to claim 1, wherein in the grating standard substance obtaining step, the photoresist material is PMMA, HSQ or ZEP, and the second substrate material is silicon, silicon nitride, aluminum or chromium.
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| CN113777685A (en) * | 2021-08-30 | 2021-12-10 | 同济大学 | Large-area self-tracing grating preparation method based on scanning atomic lithography technology |
| CN116500711A (en) * | 2023-04-14 | 2023-07-28 | 同济大学 | Two-dimensional grating standard substance with self-tracing angle and preparation method thereof |
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| CN113777685A (en) * | 2021-08-30 | 2021-12-10 | 同济大学 | Large-area self-tracing grating preparation method based on scanning atomic lithography technology |
| CN113777685B (en) * | 2021-08-30 | 2023-07-04 | 同济大学 | Large-area self-tracing grating preparation method based on scanning atomic lithography technology |
| CN116500711A (en) * | 2023-04-14 | 2023-07-28 | 同济大学 | Two-dimensional grating standard substance with self-tracing angle and preparation method thereof |
| CN116500711B (en) * | 2023-04-14 | 2024-04-26 | 同济大学 | Two-dimensional grating standard substance with self-tracing angle and preparation method thereof |
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